Climatologists from Bern University said their study also showed that concentrations of greenhouse gases are increasing at a faster rate, Swissinfo.com reported. For example, the concentration of carbon dioxide increased by 31 parts per million during one 1,600-year interval in the pre-industrial period -- its fastest growth before the industrial age -- and went up by the same amount in the past 20 years.

"The speed of climate change co-determines the impact on natural and socioeconomic systems, and the capability of adjusting and adapting to climate change," said Fortunat Joos, one of the study's authors.

The researchers analyzed atmospheric air samples and air bubbles trapped in the glacial ice. The study was published in the Proceedings of the National Academy of Sciences.